Ventilation scan. During this scan, you inhale a
radioactive tracer gas or mist. Pictures from this scan can show areas of the lungs that aren't getting enough air or that hold too much air.

Perfusion scan. During this scan, a
radioactive tracer is injected into a vein in your arm. It travels
through your blood and into the lungs. Pictures from this scan can show
areas of the lungs that aren't getting enough blood.

If the lungs are working as they should, the results of the two scans will match. If the scan results don't match, you may have a blood clot in the lung.

Ventilation and perfusion scans can be done on their own or together. If both scans are done, the test is called a
V/Q scan. The ventilation scan usually is done first.

Why It Is Done

A lung scan is done to:

Find a blood clot that is preventing normal
blood flow to part of a lung.

Check the flow of blood or air
through the lungs.

See which parts of the lungs are
working and which are damaged. This is often done before lung surgery to remove
parts of the lung.

How To Prepare

Before your lung scan, tell your
doctor if:

You are or might be pregnant.

You
are breastfeeding. The radioactive tracer used in this test can get into your breast milk. Do not breastfeed your baby for 1 or 2 days after this test. During this time, you can give your baby breast milk you stored before the test, or you can give formula. Don't use the breast milk you pump for the 1 or 2 days after the test. Throw it out.

A chest X-ray is usually done the same day, either before or
after the lung scan.

You may be asked to sign a consent form.

Talk to your doctor if you have any concerns about the
need for the test, its risks, how it will be done, or what the results will
mean. To help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).

How It Is Done

You will
need to take off any jewelry that might interfere with the scan. You may need to
take off all or most of your clothes, depending on which area is being examined. You will be given a cloth or paper covering to use during the
test.

During the scan, you might lie on your back with the
scanning camera over or under your chest. Or you might sit with the camera
next to your chest. The camera does not produce any radiation.

Ventilation scan

For the ventilation scan, a mask
will be placed over your mouth and nose. Or you may have a nose clip on your
nose and a tube in your mouth that you use for breathing. You will take a deep breath and hold it.

The camera will take pictures as the tracer moves through your lungs.

You may be asked to
breathe the gas in and out through your mouth for several minutes. You may then
be asked to hold your breath for short periods (about 10 seconds) and to change
positions. This is done so your lungs can be viewed from other angles. The camera may move to
take pictures from different angles. You need to stay very still during the
scans to avoid blurring the pictures.

Afterward, the radioactive
gas or mist will clear from your lungs as you breathe.

The
ventilation scan takes about 15 to 30 minutes.

Perfusion scan

For the perfusion scan, a small amount of the radioactive tracer is injected into your arm.

After the tracer is injected, the camera will take pictures as the tracer moves
through your lungs. The
camera may be repositioned around your chest to get different views. You need to
stay very still during the scans to avoid blurring the pictures.

The perfusion scan takes about 5 to 10 minutes.

How It Feels

Breathing through the
mask during the ventilation scan may be uncomfortable, especially if you feel very
short of breath. But you will be given plenty of oxygen through the
mask.

If you have a perfusion scan, you may feel nothing at all from the needle, or you may feel a brief sting or pinch. Otherwise, a lung scan is usually painless.

You may find it
hard to stay still. Ask for a pillow or blanket to make
yourself as comfortable as possible before the scan begins.

Risks

Allergic reactions to the radioactive
tracer are very rare. Most of the tracer will leave your body through
your urine or stool within a day. So be sure to promptly flush the toilet and
thoroughly wash your hands with soap and water. The amount of radiation is so
small that it is not a risk for people to come in contact with you after
the test.

Some people have soreness or swelling at
the injection site. A moist,
warm compress applied to the arm may help.

There is always a slight risk of
damage to cells or tissue from being exposed to any radiation, even the
low level of radiation released by the radioactive tracer used for this test. But the chance of damage is usually very low compared with the benefits of the test.

The perfusion scan is abnormal,
but the ventilation scan is normal. Depending on the difference between the two
scans, it may be a sign of a pulmonary embolism.

Both the ventilation and
perfusion scans are abnormal. This can be caused by certain types of lung
disease, such as
pneumonia or COPD, or by a pulmonary embolism.

Lung scan results can help your doctor find out how likely it is that you have a blood clot in your lung (pulmonary embolism). The results are most often
reported in one the following ways:

Normal. The results do not show any problem with
your lungs.

Low probability. The results show that the
likelihood of a blood clot is low. Your doctor may feel that you need more tests.

Indeterminate or intermediate probability. The lung
scan results show it is possible that you have a blood clot. More tests may be needed.

High probability. The results show a high likelihood of a blood clot. Your doctor will give you medicine to treat the clot.

What Affects the Test

You may not be able to have the test, or the results may not be helpful, if:

You are pregnant. The radiation from a lung scan could harm the baby.

You're not able to stay
still during the test.

You're not able to breathe through the mask or
tube.

You have a medical condition that involves the lungs or heart, such as
pulmonary edema or chronic obstructive pulmonary
disease (COPD).

What To Think About

Checking for a blood clot in your leg (deep venous thrombosis) can help your doctor decide if you are at high risk
for having one in your lung. The doctor will ask about your medical history and do a physical
exam to learn your risk level for
deep leg vein thrombosis. Then an
ultrasound is usually done. Your pretest probability
and ultrasound results will help your doctor decide which follow-up tests you need.
To learn more, see the topic
Doppler Ultrasound.

If your perfusion scan results are unclear, your doctor may want to do more tests. Pulmonary angiography is an
X-ray test that uses
contrast material injected into the bloodstream to
check the blood flow leading to the lungs. Many medical centers and doctors now use a newer CT scanning technique called CT pulmonary angiography, or CTPA.

Topic Contents

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